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May 17, 2007

Don't Know Squat???

I'm going to keep this real simple. However, if you want to dive into the details, I can't think of a better place to start than here: Milliken Research Books.

Squat occurs when the weight of an accelerating vehicle in transferred from front to back. Why do we care? Because uncorrected squat can make accelerometer-based testing tools less accurate.

Like any vehicle dynamics problem, squat can be estimated mathematically. You wanna try this on your vehicle? Thought so. If you don't want to break-out the calculator, what can you do...

Quick (lazy) Rule-of-Thumb Way: pick a fudge-factor!

The rule-of-thumb states that squat can be approximated by (x)degrees of squat per (1)-g of forward acceleration. Most guides suggest a factor of 2-degrees/g. What's the number for your vehicle? I don't know. You probably don't know either.

So how do you find it? Empirically (a fancy name for testing). Other companies that manufacture accelerometer-based test systems recommend that you take your vehicle to a drag strip, do some tests, plug in the results, and viola! A fudge factor!

Great, or is it? What if the drag strip ran slightly uphill or downhill? What if you deep-staged? What if you want to test a different vehicle? You get the idea - fudge factors apply to very narrow situations.

The g-Analyst Way: Science!

The g-Analyst uses an algorithm to estimate the squat of your vehicle without fudge factors. How do we do this? It's a secret. But I'll show you graphically how it works.

This graph represents a sweep of g's from 0 to 1.2 at five different degrees of squat. As you can see, the 2 deg/g line only tracks perfectly when the squat is 2 degrees. If the squat is more than 2 degrees, than the 2 deg/g estimate will overestimate the forward acceleration of the vehicle. Further, you can see that the g-Analyst tracks the actual vehicle acceleration nicely.